Water Quality Assessments - A Guide to Use of Biota, Sediments and Water in Environmental Monitoring - Second Edition

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Water Quality Assessments - A Guide to Use of Biota, Sediments and Water in Environmental Monitoring -

Second Edition

Edited by Deborah Chapman PUBLISHED ON BEHALF OF

UNITED NATIONSEDUCATIONAL, SCIENTIFIC AND CULTURAL ORGANIZATION WORLD HEALTHORGANIZATION

UNITED NATIONS ENVIRONMENT PROGRAMME

Published by E&FN Spon, an imprint of Chapman & Hall,

First edition 1992 Second edition 1996

Printed in Great Britain at the University Press, Cambridge ISBN 0 419 21590 5 (HB) 0 419 21600 6 (PB)

Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the UK Copyright Designs and Patents Act, 1988, this publication may not be reproduced, stored or transmitted, in any form or by any means, without the prior permission in writing of the publishers, or in the case of reprographic reproduction only in accordance with the terms of the licences issued by the Copyright Licensing Agency in the UK, or in accordance with the terms of licenses issued by the appropriate Reproduction Rights Organization outside the UK. Enquiries concerning reproduction outside the terms stated here should be sent to the publishers at the London address printed on this page.

The publisher makes no representation, express or implied, with regard to the accuracy of the information contained in this book and cannot accept any legal responsibility or liability for any errors or omissions that may be made.

A catalogue record for this book is available from the British Library

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Water Quality Assessments -

A Guide to Use of Biota, Sediments and Water in Environmental Monitoring - Second Edition

1996, 651 pages

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Foreword to the first edition

Hydrological problems related to artificial and natural changes in the quality of inland water bodies were discussed by the Co-ordinating Council of the International

Hydrological Decade (IHD) in the late 1960s. As a result, the Secretariats of UNESCO (United Nations Educational, Scientific and Cultural Organization) and WHO (World Health Organization), with the assistance of FAO (Food and Agriculture Organization of the United Nations) and IAHS (International Association for Hydrological Sciences), established an international working group, primarily to:

• identify and define the hydrological processes and phenomena directly concerned with the means of entry, distribution and self-purification of pollutants in surface and

groundwater;

• review the known effects of such pollutants on any aspect of these processes and phenomena.

The outcome of the IHD working group and their collaborators was not meant to

constitute a treatise on water chemistry or water pollution problems, but was a document attempting to link water quality considerations to aspects of the quantitative hydrology of surface and groundwater bodies. Advice was also included on the organisation of hydrological services, methods of conducting water quality surveys, and interpretation and evaluation of water quality data for hydrological purposes. An attempt was also made to meet the needs of developing regions by describing methods likely to be applied in these regions, both from the point of view of practicability and economy. On the other hand the report also aimed to be attractive to industrialised countries by including references to sophisticated methods.

It appeared that many hydrologists found difficulty in coping with water quality problems, and that hydrological surveys and water quality studies were not often adequately linked.

The joint UNESCO/WHO publication Water Quality Surveys (1978) was, therefore, intended to harmonise these aspects and to synthesise the assessment of the hydrological regime and quality changes brought about by nature and man. The publication became a success world-wide and soon ran out of stock. The two Secretariats of UNESCO and WHO considered a re-print of the 1978 version, but decided to compile a completely new edition in view of the following:

(a) The progress in water quality research had been enormous over the past years and this needed to be taken into account.

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(b) Water quality had become a regional, if not a global, concern encompassing more pollutants than in the past; an ecological approach could combine the physical, chemical, biological and microbiological aspects; x Water Quality Assessments heavy metals and synthetic organic compounds have called for a change in the strategies for water quality surveys and monitoring.

(c) There is no need to describe the operational aspects of water quality monitoring and the laboratory procedures since they are mostly contained in the GEMS/WATER

Operational Guide, a revised third edition of which appeared in 1991.

(d) Basic guidance on methodology is given in the GEMS/WATER Handbook for Water Quality Monitoring in Developing Countries which will be available by the end of 1991.

In October 1987, the two Secretariats compiled an annotated outline for the revised Water Quality Surveys on the understanding that the new book would describe, in a much broader way, the application and interpretation of water quality information in water resource management. The methodological and technical aspects could be largely omitted since the reader could be referred to the above-mentioned GEMS/WATER literature.

Authors were designated in 1988 and a first meeting of authors and contributors, supported by the United Nations Environment Programme (UNEP) and the USSR Centre for International Projects, took place in Sochi (former USSR) from 14 to 20 November 1988, followed by a second editorial meeting at Baikalsk (former USSR) from 3 to 10 August 1990. A final editorial panel meeting was then convened in Geneva, 22- 23 November 1990. The result of these meetings is this guidebook, now renamed Water Quality Assessments.

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Foreword to the second edition

Much has happened in the water sector at national and international level since the preparation of the first edition of this guidebook. One major event was the International Conference on Water and the Environment which was held in January 1992 in Dublin, Ireland. In dealing with the protection of water resources, water quality and aquatic ecosystems, the conference made rather specific requests regarding the need for more and better water quality assessments, including:

• Purpose-orientated water assessments and predictions, taking into account the specificity of both surface and groundwaters, water quality and water quantity, and addressing all pollution types.

• Assessments harmonised for natural basins or catchments (including station networks, field and laboratory techniques, methodologies and procedures, and data handling) and leading to basin-wide data systems.

• New appropriate assessment and prediction techniques and methodologies, such as low-cost field measurements, continuous and automatic monitoring, use of biota and sediment for micro-pollution monitoring, remote sensing, and geographic information systems.

In June 1992 in Rio de Janeiro, Brazil, the United Nations Conference on Environment and Development resulted in an agreement on the action plan known as Agenda 21 which, in its chapter on freshwater, largely endorsed the recommendations from the Dublin conference. The stated objectives of Agenda 21 include issues which this guidebook aims to address, specifically:

• to make available to all countries water resources assessment technology that is appropriate to their needs, irrespective of their level of development, and

• to have all countries establish the institutional arrangements needed to ensure the efficient collection, processing, storage, retrieval and dissemination to users of information about the quality and quantity of available water resources, at the level of catchments and groundwater aquifers, in an integrated manner.

The concerns expressed at these conferences, together with the feedback from readers and users of the first edition of this guidebook, have guided the editor and authors in preparing the second edition. Latest developments in strategies, as well as on

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technologies and methods, have been taken into account to make the book useful for water resources managers charged with the monitoring, assessment and control of water quality for a variety of purposes. Thus this guidebook should contribute to the capacity building initiatives launched in a number of countries in the aftermath of the Rio de Janeiro conference by supporting the scientifically-sound assessment of water resources which are tending to become more sparse and polluted.

One major change from the first edition, which is in addition to the general review and updating, is the introduction of a new chapter on reservoirs. The construction of dams along many rivers has increased rapidly over recent years, including some more controversial large dam projects. The multiple use of the resulting reservoirs requires a sound water quality assessment component to their management strategies. A separate chapter has been devoted to reservoirs because many have complex hydrodynamic features and all are subject to potential or actual human intervention in their natural chemical and physical processes. The original rivers and lakes chapters of the first edition have been modified accordingly.

The other major development in preparing the second edition concerns the production of the companion handbook Water Quality Monitoring: a practical guide to the design and implementation of freshwater quality studies and monitoring programmes. The

manuscript for the Water Quality Monitoring handbook emerged and was finalised in parallel to the second edition of this guidebook. Water Quality Monitoring provides the practical and methodological details whereas Water Quality Assessments gives the overall strategy for assessments of the quality of the main types of water body. Together the two books cover all the major aspects of water quality, its measurement and its evaluation.

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Summary and scope

This guidebook concentrates on the process of setting up monitoring programmes for the purpose of providing a valid data base for water quality assessments. The choice of variables to be measured in the water, the sediment and in biota are described in Chapters 3, 4 and 5 and the common procedures for data handling and presentation in Chapter 10. Interpretation of these data for the purpose of assessing water quality in rivers, lakes, reservoirs and groundwaters is presented in Chapters 6, 7, 8 and 9 respectively. These chapters, specific to the type of water body, focus on monitoring strategies, requirements for water quality and quantity data and interpretative techniques.

The choice of the appropriate methods is illustrated by case studies for typical water pollution situations. In view of the varying levels of resources which countries can put at the disposal of this activity, the strategies for water quality assessment are developed according to three different levels of monitoring operations: simple, intermediate and advanced.

For the purpose of this presentation of water quality assessment techniques the following types of water resources have been taken into consideration:

• Rivers and streams of all sizes from source to tidal limit (i.e. the influence of salt water intrusion). Canals and inter-connecting river systems are also included.

• Lakes of all sizes and types, including marshes and bogs.

• Reservoirs of various types, especially river impoundments.

• Groundwaters of various types, shallow or deep, and phreatic or confined.

These types of water bodies include all major freshwater resources subject to

anthropogenic influences or intentionally used for municipal or industrial supply, irrigation, recreation, cooling or other purposes. However, certain types of waters are outside the scope of this book, including: estuaries, coastal lagoons, salt marshes and other saline waters, wastewaters of different origins, thermal and mineral springs, saline aquifers, brines and atmospheric precipitation such as rain and snow.

Within the range of water quality issues addressed in this guidebook efforts have been concentrated on major areas of vital importance. Several complementary publications

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are readily available which cover other specific aspects in great detail and, when referred to, their use in conjunction with the present guide is strongly recommended.

There are no geographical limits imposed on the applicability of the guidance provided in this book since an effort was made by the authors to address all kinds of environmental conditions occurring in aquatic ecosystems world-wide. Thus, the specific situations of humid and dry tropics, as well as of mountainous and lowland waters, in water abundant or semi-arid and arid climatic zones, are all covered by means of examples. Attempts have been made to find examples from all world regions but, inevitably, there is more literature available from the developed world than the developing world and this is

reflected in the reference lists attached to each chapter. Water quality, and its monitoring and assessment, is also greatly influenced by the size of the water body and, therefore, relevant guidance is provided for different levels of magnitude.

Within this guidebook various water quality problems (organic pollution, eutrophication, acidification, toxic contamination etc.) and their related descriptors are discussed at various levels of complexity. Chemical constituents and contaminants, as well as the biological characteristics of water bodies, are covered extensively. However, the

consequences of temperature changes due to thermal discharges are only addressed in relation to their effects on aquatic life.

Human health is affected, in many world regions, by vector-transmitted diseases

associated with vector organisms which breed in the aquatic environment. This problem is enormous since there are 200 million people suffering from one such disease alone, i.e. schistosomiasis. However, since the occurrence of such diseases, and their

containment, is closely linked to water resource development projects, rather than to pollution sources and effects, this issue is not dealt with in this book. Further information on these topics can be found in the internationally recognised literature on the subject (WHO, 1980, 1982, 1983).

Pathogenic agents causing water-borne diseases include bacteria and viruses as well as protozoa and helminths. Although they interfere only marginally with aquatic life in general, they cause severe public health problems and are considered responsible for most of the infant mortality in developing countries. Monitoring is usually done indirectly by identifying and quantifying indicators of faecal pollution such as the coliform groups.

This guidebook follows the same concept and interested readers are referred to further background information in the relevant literature published by the World Health

Organization (WHO, 1976, 1985, 1993).

Radioactive isotopes, natural or man-made, are not included in this publication because the monitoring of radiation is covered by the work of the International Atomic Energy Agency (IAEA).

The basic methods, procedures, techniques, field equipment and analytical instruments required to monitor water quality have been developed and field-tested in a wide range of situations over the last two decades. A wealth of experience has been accumulated and communicated through guidebooks and reports on water quality. As a consequence, the authors of this book felt that the monitoring methods and procedures already

published adequately cover the necessary techniques. Therefore, they have

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concentrated more on the principles, approaches and design for water quality assessment and on the interpretation of the resulting data.

With respect to the field operations for monitoring, a comprehensive and practical booklet has been produced by the World Meteorological Organization (WMO, 1988). It describes essential factors to consider in monitoring such as the location of sampling sites, the collection of surface water samples, field measurements, sampling for

biological analysis, shipment of samples, field safety and training programmes related to all of the above. Similar publications are not widely available for groundwaters but a description of techniques is given in Barcelona et al. (1985). The international project on global freshwater quality monitoring, GEMS/WATER (WHO, 1991), has based its

monitoring operations on a practical guidebook, the GEMS/WATER Operational Guide (WHO, 1992) which gives in detail information on site selection, sampling, analysis, quality control and data processing. Most chemical analyses required for water quality monitoring are adequately covered by such reference books, whereas non-standardised methods for biological monitoring have to be developed for local or regional situations.

However, although analytical reference methods are given in several general

publications, it is also necessary to consult the International Standards Organization (ISO) “Standard methods” series of publications and to refer to recognised national publications, such as the standard methods produced by the American Public Health Association (APHA, 1989), the German standard methods (Deutsche Einheitsverfahren zur Wasser-, Abwasser und Schlammuntersuchung (DIN)) and those of the USSR State Committee for Hydrometeorology and Environmental Control (1987, 1989) which are now used in Russia and other CIS countries.

Hydrological measurements are an indispensable accompaniment to any surface water quality monitoring operation. Groundwater quality data also require adequate

hydrological information for any meaningful interpretation. The World Meteorological Organization has developed practical guidelines as part of its Operational Hydrology Programme (WMO, 1994) and the United Nations Educational, Scientific and Cultural Organization (UNESCO) has also issued groundwater hydrology guidebooks. These publications provide methodology for water quality data collection, interpretation and presentation (UNESCO, 1983).

References

APHA 1989 Standard Methods for the Examination of Water and Wastewater. 17th edition, American Public Health Association, Washington D.C., 1,268 pp.

Barcelona, M.J., Gibb, J.P., Helfrich, J.A. and Garske, E.E. 1985 Practical Guide for Groundwater Sampling. ISWS Contract Report 374, Illinois State Water Survey, Champaign, Illinois, 94 pp.

UNESCO 1983 International Legend for Hydrogeological Maps. Technical Documents in Hydrology, SC.841/S7, United Nations Educational Scientific and Cultural Organization, Paris, 51 pp.

USSR State Committee for Hydrometeorology and Environmental Control 1987 Methods for Bioindication and Biotesting in Natural Waters. Volume 1. Hydrochemical Institute, Leningrad, 152 pp.

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USSR State Committee for Hydrometeorology and Environmental Control 1989 Methods for Bioindication and Biotesting in Natural Waters. Volume 2. Hydrochemical Institute, Leningrad, 275 pp, [In Russian].

WHO 1976 Surveillance of Drinking-Water Quality. WHO Monograph Series No. 63, World Health Organization, Geneva, 128 pp.

WHO 1980 Environmental Management for Vector Control. Fourth report of the WHO Expert Committee on Vector Biology and Control, Technical Report Series No. 649, World Health Organization, Geneva, 67 pp.

WHO 1982 Manual for Environmental Management for Mosquito Control, with Special Emphasis on Malaria Vectors. WHO Offset Publication No. 66, World Health

Organization, Geneva, 281 pp.

WHO 1983 Integrated Vector Control. Seventh report of the WHO Expert Committee on Vector Biology and Control, Technical Report Series No. 688, World Health Organization, Geneva, 72 pp.

WHO 1985 Guidelines for Drinking-Water Quality, Volume 3, Drinking-Water Quality Control in Small-Community Supplies. World Health Organization, Geneva, 120 pp.

WHO 1991 GEMS/WATER 1990-2000. The Challenge Ahead. WHO/PEP/91.2, World Health Organization, Geneva.

WHO 1992 GEMS/WATER Operational Guide. Third edition. World Health Organization, Geneva.

WHO 1993 Guidelines for Drinking-Water Quality, Volume 1, Recommendations.

Second edition. World Health Organization, Geneva, 130 pp.

WMO 1988 Manual on Water Quality Monitoring. WMO Operational Hydrology Report, No. 27, WMO Publication No. 680, World Meteorological Organization, Geneva, 197 pp.

WMO 1994 Guide to Hydrological Practices. Fifth edition, WMO Publication No. 168, World Meteorological Organization, Geneva, 735 pp.

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Acknowledgements

The co-sponsoring organisations would like to thank and acknowledge the time and effort contributed by many people, all of whom have helped to ensure the smooth and efficient production of this book. A number of authors provided material and, in many cases, several authors and their collaborators have worked on the same sections. As it is difficult to identify adequately the contribution of each individual author in the chapter headings, the names of the principal contributors, to whom we are greatly indebted, are listed below:

Albert Beim, Institute of Ecological Toxicology, Ministry of Environmental Protection and Natural Resources of Russia, Baikalsk, Russia (Chapters 5 and 7)

Deborah Chapman, Environment Consultant, Kinsale, Ireland (Chapters 3, 5 and 6) John Chilton, British Geological Survey, Wallingford, UK (Chapter 8)

Adrian Demayo, Environment Canada, Ottawa, Canada (Chapter 9)

Günther Friedrich, Landesamt für Wasser und Abfall N.W., Dusseldorf, Germany (Chapters 5 and 6)

Richard Helmer, World Health Organization, Geneva, Switzerland (Chapters 1 and 2) Vitaly Kimstach, Arctic Monitoring and Assessment Programme, Oslo, Norway (Chapters 2 and 3)

Michel Meybeck, Université de Pierre et Marie Curie, Paris, France (Chapters 1, 2, 4, 6 and 7)

Walter Rast, United Nations Environment Programme, Nairobi, Kenya (Chapter 8) Alan Steel, Water Supply Consultant, Kinsale, Ireland (Chapters 8 and 10)

Richard Thomas, Waterloo Centre for Groundwater Research, Waterloo, Canada (Chapters 4, 6 and 7)

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Jeff Thornton, International Environmental Management Services Limited, Waukesha, USA (Chapter 8)

Messrs R. Helmer (WHO) and W.H. Gilbrich (UNESCO) provided the Secretariat services for the meetings and were responsible for the arrangements for the initial compilation of manuscripts and all meetings. Ms J. Kenny (WHO) provided secretarial and administrative assistance throughout. The co-sponsoring organisations are also greatly indebted to Michel Meybeck for his advice and efforts in the preparation of the revision of the outline for this book and to Richard Thomas for chairing the authors’

meetings.

Thanks are also due to Dave Rickert (U.S. Geological Survey, Reston, VA) for his thorough review of the final manuscript, to Walter Rast (UNEP) for his advice on the second edition, and to Deborah Chapman who undertook the laborious tasks of editing the whole manuscript and management of the production of camera-ready copy and publication of the book.

The additional services of Imogen Bertin (typesetting, design and layout) and Alan Steel (graphics, editorial assistance), as well as those who reviewed and supplied material for several chapters, are gratefully acknowledged.

The printing of colour Figures 6.34 and 6.35 was financially supported by the IHP/OHP National Committee of the Federal Republic of Germany, and of colour Figures 7.10 and 7.11 by the National Water Research Institute, Environment Canada.

The book is a contribution to UNESCO’s International Hydrological Programme and to the UNEP/WHO/WMO/UNESCO co-sponsored GEMS/WATER programme. The UN agencies are greatly indebted to the authors, and to the former USSR institutes which hosted their meetings.

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Abbreviations used in text

AAS Atomic absorption spectrophotometry AES Atomic emission spectrophotometry ANC Acid neutralising capacity

ANOVA Analysis of variance AOX Adsorbable organic halides

APHA American Public Health Association AQC Analytical quality control

ASPT Average Score Per Taxon

BMWP Biological Monitoring Working Party-score BOD Biochemical oxygen demand

CEC Commission of the European Communities

CIPEL International Surveillance Commission of Lake Geneva COD Chemical oxygen demand

DDT Dichlorodiphenyltrichloroethane

DIN Deutsche Einheitsverfahren zur Wasser-, Abwasser und Schlammuntersuchung DO Dissolved oxygen

DOC Dissolved organic carbon DON Dissolved organic nitrogen

EDTA Ethylenediaminetetraacetic acid

EIFAC European Inland Fisheries Advisory Commission EQI Ecological Quality Index

EU European Union (formerly European Community) FAO Food and Agriculture Organization of the United Nations GC Gas chromatograph(y)

GC/MS Gas chromatography/mass spectrometry GEMS Global Environment Monitoring System GIS Geographic information systems

GLOWDAT GLObal Water DATa Management System IAEA International Atomic Energy Agency

IAHS International Association for Hydrological Science IC Ion chromatography

ICP/AES Inductively coupled plasma atomic emission spectrometry

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ICPS Inductively coupled plasma spectroscopy IHD International Hydrological Decade IR Infra red

IRPTC International Register of Potentially Toxic Chemicals ISO International Standards Organization

JTU Jackson turbidity units

LC Liquid chromatography LOD Limit-of-detection

LOWESS Locally weighted scatter plot smoothing LT Less than values

MAC Maximum allowable concentration MATC Maximum allowable toxic concentration MCNC Most common natural concentrations MLE Maximum likelihood estimator MPN Most probable number

MS Mass spectrometer (spectrometry)

NAQUADAT The NAtional Water QUALity Accounting DATa Bank(Canada) NCPB National Contaminant Biomonitoring Program (USA)

ND Not detected

NOEC No observed effect concentration NTU Nephelometric turbidity units

OECD Organisation for Economic Co-operation and Development OII Odour intensity index

OPP Oxygen Production Potential PA Apatitic phosphorus

PAH Polychlorinated aromatic hydrocarbons PCA Principal components analysis

PCBs Polychlorinated biphenyls PCs Personal computers PFU Plaque forming units

PINA Non-apatitic inorganic phosphorus PM Particulate matter PO Organic phosphorus POC Particulate organic carbon PON Particulate organic nitrogen PTFE Polytetrafluoroethylene

RAISON Regional Analysis by Intelligent Systems on a Microcomputer RCRA Resource Conservation and Recovery Act, USA

RIVPACS River In Vertebrate Prediction and Classification System SA Sediment accretion

SAR Sodium adsorption ratio SEF Sediment enrichment factor SM Suspended matter SOE State of the Environment

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SR Settling rate SRP Soluble reactive phosphorus TAC Total absorbance colour TCDD Tetra chlorinated dibenzo dioxin TDS Total dissolved solids

TOC Total organic carbon TP Total phosphorus TSS Total suspended solids

UNEP United Nations Environment Programme

UNESCO United Nations Educational, Scientific and Cultural Organization US EPA United States Environmental Protection Agency

UV Ultra violet VA Voltammetry

WASP Water Analysis Simulation Programme WHO World Health Organization

WMO World Meteorological Organization

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**Chapter 1* - AN INTRODUCTION TO WATER QUALITY**

*This chapter was prepared by M. Meybeck and R. Helmer

1.1. Characterisation of water bodies

Water bodies can be fully characterised by the three major components: hydrology, physico-chemistry, and biology. A complete assessment of water quality is based on appropriate monitoring of these components.

1.1.1. Hydrodynamic features

All freshwater bodies are inter-connected, from the atmosphere to the sea, via the hydrological cycle. Thus water constitutes a continuum, with different stages ranging from rainwater to marine salt waters. The parts of the hydro-logical cycle which are considered in this book are the inland freshwaters which appear in the form of rivers, lakes or groundwaters. These are closely inter-connected and may influence each other directly, or through intermediate stages, as shown in Table 1.1 and Figure 1.1. Each of the three principal types of water body has distinctly different hydrodynamic properties as described below.

Rivers are characterised by uni-directional current with a relatively high, average flow velocity ranging from 0.1 to 1 m s^-1. The river flow is highly variable in time, depending on the climatic situation and the drainage pattern. In general, thorough and continuous vertical mixing is achieved in rivers due to the prevailing currents and turbulence. Lateral mixing may take place only over considerable distances downstream of major

confluences.

Lakes are characterised by a low, average current velocity of 0.001 to 0.01 m s^-1 (surface values). Therefore, water or element residence times, ranging from one month to several hundreds of years, are often used to quantify mass movements of material. Currents within lakes are multi-directional. Many lakes have alternating periods of stratification and vertical mixing; the periodicity of which is regulated by climatic conditions and lake depth.

Groundwaters are characterised by a rather steady flow pattern in terms of direction and velocity. The average flow velocities commonly found in aquifers range from 10^-10 to 10^-3 m s^-1 and are largely governed by the porosity and permeability of the geological material.

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As a consequence mixing is rather poor and, depending on local hydrogeological features, the ground-water dynamics can be highly diverse.

There are several transitional forms of water bodies which demonstrate features of more than one of the three basic types described above and are characterised by a particular combination of hydrodynamic features. The most important transitional water bodies are illustrated in Figure 1.1 and are described below.

Table 1.1. The hydrological cycle: water volumes, residence times and fluxes Total cycle

volume (10⁶ Km³)

(%)

Freshwater volume only (%)

Freshwater volume without icecaps and

glaciers (%)

Residence times

Oceans and seas

1,370 94 ~4,000 years

Lakes and reservoirs

0.13 <

0.01

0.14 0.21 ~10 years

Swamps and marshes

< 0.01 <

0.01

< 0.01 < 0.01 1-10 years River channels < 0.01 <

0.01

< 0.01 < 0.01 ~2 weeks Soil moisture 0.07 <

0.01

0.07 0.11 2 weeks-1

year Groundwater 60 4 66.5 99.65 2 weeks-

50,000 years Icecaps and

glaciers

30 2 33.3 10-1,000 years

Atmospheric water

0.01 <

0.01

0.01 0.02 ~10 days

Biospheric water < 0.01 <

0.01

< 0.01 < 0.01 ~1 week Fluxes

Evaporation from

oceans 425 Evaporation from

land

71 Precipitation

from oceans

385 Precipitation

from land

111 Run-off to

oceans

37.4 Glacial ice 2.5

Source: Modified from Nace, 1971 and various sources

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Reservoirs are characterised by features which are intermediate between rivers and lakes. They can range from large-scale impoundments, such as Lake Nasser, to small dammed rivers with a seasonal pattern of operation and water level fluctuations closely related to the river discharge, to entirely constructed water bodies with pumped in-flows and out-flows. The cascade of dams along the course of the River Dnjepr is an example of the interdependence between rivers and reservoirs. The hydrodynamics of reservoirs are greatly influenced by their operational management regime.

Flood plains constitute an intermediate state between rivers and lakes with a distinct seasonal variability pattern. Their hydrodynamics are, however, determined by the river flow regime.

Marshes are characterised by the dual features of lakes and phreatic aquifers. Their hydrodynamics are relatively complex.

Figure 1.1. Inter-connections between inland freshwater bodies (intermediate water bodies have mixed characteristics belonging to two or three of the major

water bodies)

Alluvial and karstic aquifers are intermediate between rivers and ground-waters. They differ, generally, in their flow regime which is rather slow for alluvial and very rapid for karstic aquifers. The latter are often referred to as underground rivers.

As a consequence of the range of flow regimes noted above, large variations in water residence times occur in the different types of inland water bodies (Figure 1.2). The

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hydrodynamic characteristics of each type of water body are highly dependent on the size of the water body and on the climatic conditions in the drainage basin. The governing factor for rivers is their hydrological regime, i.e. their discharge variability.

Lakes are classified by their water residence time and their thermal regime resulting in varying stratification patterns. Although some reservoirs share many features in common with lakes, others have characteristics which are specific to the origin of the reservoir.

One feature common to most reservoirs is the deliberate management of the inputs and/or outputs of water for specific purposes. Groundwaters greatly depend upon their recharge regime, i.e. infiltration through the unsaturated aquifer zone, which allows for the renewal of the ground-water body. Further details for each of these water bodies are available in Chapters 6, 7, 8 and 9.

Figure 1.2. Water residence time in inland freshwater bodies (After Meybeck et al., 1989)

It cannot be over-emphasised that thorough knowledge of the hydrodynamic properties of a water body must be acquired before an effective water quality monitoring system can be established. Interpretation of water quality data cannot provide meaningful conclusions unless based on the temporal and spatial variability of the hydrological regime.

1.1.2. Physical and chemical properties

Each freshwater body has an individual pattern of physical and chemical characteristics which are determined largely by the climatic, geomorphological and geochemical conditions prevailing in the drainage basin and the underlying aquifer. Summary

characteristics, such as total dissolved solids, conductivity and redox potential, provide a general classification of water bodies of a similar nature. Mineral content, determined by the total dissolved solids present, is an essential feature of the quality of any water body resulting from the balance between dissolution and precipitation. Oxygen content is another vital feature of any water body because it greatly influences the solubility of

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metals and is essential for all forms of biological life. For a complete description of chemical water quality variables see Chapter 3.

The chemical quality of the aquatic environment varies according to local geology, the climate, the distance from the ocean and the amount of soil cover, etc. If surface waters were totally unaffected by human activities, up to 90-99 per cent of global freshwaters, depending on the variable of interest, would have natural chemical concentrations suitable for aquatic life and most human uses. Rare (between 1 and 10 per cent and between 90 and 99 per cent of the global distribution) and very rare (< 1 per cent and >

99 per cent of the global distribution - see section 1.3, Figure 1.4) chemical conditions in freshwaters, such as occur in salt lakes, hydrothermal waters, acid volcanic lakes, peat bogs, etc., usually make the water unsuitable for human use (see section 1.3).

Nonetheless, a range of aquatic organisms have adapted to these extreme

environments. In many regions groundwater concentrations of total dissolved salts, fluoride, arsenic, etc., may also naturally exceed maximum allowable concentrations (MAC) (see section 9.2.6).

Particulate matter (PM) is a key factor in water quality, regulating adsorption-desorption processes. These processes depend on: (i) the amount of PM in contact with a unit water volume, (ii) the type and character of the PM (e.g. whether organic or inorganic), and (iii) the contact time between the water and the PM. The time variability of dissolved and particulate matter content in water bodies results mainly from the interactions between hydro-dynamic variability, mineral solubility, PM characteristics and the nature and intensity of biological activity.

1.1.3. Biological characteristics

The development of biota (flora and fauna) in surface waters is governed by a variety of environmental conditions which determine the selection of species as well as the

physiological performance of individual organisms. A complete description of biological aspects of water quality is presented in Chapter 5. The primary production of organic matter, in the form of phytoplankton and macrophytes, is most intensive in lakes and reservoirs and usually more limited in rivers. The degradation of organic substances and the associated bacterial production can be a long-term process which can be important in groundwaters and deep lake waters which are not directly exposed to sunlight.

In contrast to the chemical quality of water bodies, which can be measured by suitable analytical methods, the description of the biological quality of a water body is a

combination of qualitative and quantitative characterisation. Biological monitoring can generally be carried out at two different levels:

• the response of individual species to changes in their environment or,

• the response of biological communities to changes in their environment.

Water quality classification systems based upon biological characteristics have been developed for various water bodies. The chemical analysis of selected species (e.g.

mussels and aquatic mosses) and/or selected body tissues (e.g. muscle or liver) for contaminants can be considered as a combination of chemical and biological monitoring.

Biological quality, including the chemical analysis of biota, has a much longer time

dimension than the chemical quality of the water since biota can be affected by chemical,

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and/or hydro-logical, events that may have lasted only a few days, some months or even years before the monitoring was carried out.

1.2. Definitions related to water quality

In view of the complexity of factors determining water quality, and the large choice of variables used to describe the status of water bodies in quantitative terms, it is difficult to provide a simple definition of water quality. Furthermore, our understanding of water quality has evolved over the past century with the expansion of water use requirements and the ability to measure and interpret water characteristics. Figure 1.3 demonstrates the evolutionary nature of chemical water quality issues in industrialised countries. For the purposes of this guidebook the following definitions have been accepted:

Term Definition

QUALITY of the aquatic environment

• Set of concentrations, speciations, and physical partitions of inorganic or organic substances.

• Composition and state of aquatic biota in the water body.

• Description of temporal and spatial variations due to factors internal and external to the water body.

POLLUTION of the aquatic environment

Introduction by man, directly or indirectly, of substances or energy which result in such deleterious effects as:

• harm to living resources,

• hazards to human health,

• hindrance to aquatic activities including fishing,

• impairment of water quality with respect to its use in agricultural, industrial and often economic activities, and

• reduction of amenities¹

1 as defined by GESAMP (1988)

The physical and chemical quality of pristine waters would normally be as occurred in pre-human times, i.e. with no signs of anthropogenic impacts. The natural

concentrations (governed by factors described in section 1.1.2) could, nevertheless, vary by one or more orders of magnitude between different drainage basins. In practice, pristine waters are very difficult to find as a result of atmospheric transport of

contaminants and their subsequent deposition in locations far distant from their origin.

Before pristine waters reach the polluted condition, two phases of water quality degradation occur.

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Figure 1.3. The sequence of water quality issues arising in industrialised countries (After Meybeck and Helmer, 1989)

The first phase shows an alteration in water quality with evidence of human impact but without any harm to the biota or restriction of water use. Such changes may only be detectable by repeated chemical measurements over long time spans. Typical examples are when Cl^- concentrations change from a few mg l^-1 to 10 mg l^-1 (as in Lake Geneva where average concentrations went from 2 mg l^-1 in 1960 to 6 mg l^-1 at present) or when N-NO3^- concentrations change from 0.1 mg l^-1 to 0.2 mg l^-1. The next phase consists of some degradation of water quality and possible restriction of specific water uses because recommended water quality guidelines (local, regional or global) may be

exceeded. Once maximum acceptable concentrations for selected variables in relation to water use have been exceeded, or the aquatic habitat and biota have been markedly modified, the water quality is usually defined as polluted (see example in section 6.7.3).

Description of the quality of the aquatic environment can be carried out in a variety of ways. It can be achieved either through quantitative measurements, such as physico- chemical determinations (in the water, particulate material, or biological tissues) and biochemical/biological tests (BOD measurement, toxicity tests, etc.), or through semi- quantitative and qualitative descriptions such as biotic indices, visual aspects, species inventories, odour, etc. (see Chapters 3, 4 and 5). These determinations are carried out in the field and in the laboratory and produce various types of data which lend

themselves to different interpretative techniques (see section 10.3.1). For the purpose of simplicity the term “water quality” is used throughout this book, although it refers to the overall quality of the aquatic environment.

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The terms monitoring and assessment are frequently confused and used synonymously.

For the purpose of this guidebook and its companion handbook (Bartram and Ballance, 1996) the following definitions are used:

Term Definition

Water quality ASSESSMENT

The overall process of evaluation of the physical, chemical and biological nature of water in relation to natural quality, human effects and intended uses, particularly uses which may affect human health and the health of the aquatic system itself.

Water quality MONITORING

The actual collection of information at set locations and at regular intervals in order to provide the data which may be used to define current conditions, establish trends, etc.

Water quality assessment includes the use of monitoring to define the condition of the water, to provide the basis for detecting trends and to provide the information enabling the establishment of cause-effect relationships. Important aspects of an assessment are the interpretation and reporting of the results of monitoring and the making of

recommendations for future actions (see Chapter 2). Thus there is a logical sequence consisting of three components: monitoring, followed by assessment, followed by

management. In addition, there is also a feedback loop because management inevitably requires compliance monitoring to enforce regulations, as well as assessments at periodic intervals to verify the effectiveness of management decisions. The principal objective of the global freshwater quality monitoring project, GEMS/WATER, provides an illustrative example of the complexity of the assessment task and its relation to

management (WHO, 1991):

• To provide water quality assessments to governments, the scientific community and the public, on the quality of the world’s freshwater relative to human and aquatic ecosystem health, and global environmental concerns, specifically:

• to define the status of water quality;

• to identify and quantify trends in water quality;

• to define the cause of observed conditions and trends;

• to identify the types of water quality problems that occur in specific geographical areas;

and

• to provide the accumulated information and assessments in a form that resource management and regulatory agencies can use to evaluate alternatives and make necessary decisions.

1.3. Anthropogenic impacts on water quality

With the advent of industrialisation and increasing populations, the range of

requirements for water have increased together with greater demands for higher quality water. Over time, water requirements have emerged for drinking and personal hygiene, fisheries, agriculture (irrigation and livestock supply), navigation for transport of goods, industrial production, cooling in fossil fuel (and later also in nuclear) power plants,

hydropower generation, and recreational activities such as bathing or fishing. Fortunately, the largest demands for water quantity, such as for agricultural irrigation and industrial cooling, require the least in terms of water quality (i.e. critical concentrations may only be

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set for one or two variables). Drinking water supplies and specialised industrial manufacturers exert the most sophisticated demands on water quality but their

quantitative needs are relatively moderate. In parallel with these uses, water has been considered, since ancient times, the most suitable medium to clean, disperse, transport and dispose of wastes (domestic and industrial wastes, mine drainage waters, irrigation returns, etc.).

Each water use, including abstraction of water and discharge of wastes, leads to specific, and generally rather predictable, impacts on the quality of the aquatic environment (see Chapter 3). In addition to these intentional water uses, there are several human activities which have indirect and undesirable, if not devastating, effects on the aquatic

environment. Examples are uncontrolled land use for urbanisation or deforestation, accidental (or unauthorised) release of chemical substances, discharge of untreated wastes or leaching of noxious liquids from solid waste deposits. Similarly, the

uncontrolled and excessive use of fertilisers and pesticides has long-term effects on ground and surface water resources.

Structural interventions in the natural hydrological cycle through canalisation or damming of rivers, diversion of water within or among drainage basins, and the over-pumping of aquifers are usually undertaken with a beneficial objective in mind. Experience has shown, however, that the resulting long-term environmental degradation often outweighs these benefits. The most important anthropogenic impacts on water quality, on a global scale, are summarised in Table 1.2, which also distinguishes between the severity of the impairment of use in different types of water bodies.

Table 1.2. Major freshwater quality issues at the global scale¹ Water body Issue

Rivers Lakes Reservoirs Groundwaters

Pathogens xxx x² x² x

Suspended solids xx na x na Decomposable organic matter³ xxx x xx x

Eutrophication⁴ x xx xxx na

Nitrate as a pollutant x 0 0 xxx

Salinisation x 0 x xxx

Trace elements xx xx xx xx⁵ Organic micropollutants xxx xx xx xxx⁵

Acidification x xx xx 0

Modification of hydrological regimes⁶ xx x x

A full discussion of the sources and effects of each of these pollution issues is available in the relevant chapters of Meybeck et al., 1989

xxx Severe or global deterioration found xx Important deterioration

x Occasional or regional deterioration

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0 Rare deterioration na Not applicable

1 This is an estimate for the global scale. At a regional scale these ranks may vary greatly according to the stage of economic development and land-use. Radioactive and thermal wastes are not considered here.

2 Mostly in small and shallow water bodies

3 Other than resulting from aquatic primary production

4 Algae and macrophytes

5 From landfill, mine tailings

6 Water diversion, damming, overpumping, etc.

Pollution and water quality degradation interfere with vital and legitimate water uses at any scale, i.e. local, regional or international (Meybeck et al., 1989). As shown in Table 1.3, some types of uses are more prone to be affected than others. Water quality criteria, standards and the related legislation are used as the main administrative means to manage water quality in order to achieve user requirements. The most common national requirement is for drinking water of suitable quality, and many countries base their own standards on the World Health Organization (WHO) guidelines for drinking water quality (WHO, 1984, 1993). In some instances, natural water quality (particularly conditions which occur very rarely; see section 1.1.2) is inadequate for certain purposes as defined by recommended or guideline concentrations (Figure 1.4B). However, other water bodies may still be perfectly usable for some activities even after their natural conditions have been altered by pollution. A very comprehensive collection and evaluation of water quality criteria for a variety of uses has been made, and is being regularly updated, by Canadian scientists (Environment Canada, 1987).

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Table 1.3. Limits of water uses due to water quality degradation Use

Pollutant

Drinking water

Aquatic wildlife, fisheries

Recreation Irrigation Industrial uses

Power and cooling

Transport

Pathogens xx 0 xx x xx¹ na na

Suspended solids

xx xx xx x x x² xx³

Organic matter xx x xx + xx⁴ x⁵ na Algae x^5,6 x⁷ XX + xx⁴ x⁵ x⁸

Nitrate xx x na + xx¹ na na

Salts⁹ xx xx na xx xx¹⁰ na na Trace elements xx xx x x x na na Organic

micropollutants

xx xx x x ? na na Acidification x xx x ? x x na xx Marked impairment causing major treatment or excluding the desired use

x Minor impairment 0 No impairment na Not applicable

+ Degraded water quality may be beneficial for this specific use

? Effects not yet fully realised

1 Food industries

2 Abrasion

3 Sediment settling in channels

4 Electronic industries

5 Filter dogging

6 Odour, taste

7 In fish ponds higher algal biomass can be accepted

8 Development of water hyacinth (Eichhomia crassipes)

9 Also includes boron, fluoride, etc.

10 Ca, Fe, Mn in textile industries, etc.

Due to the complexity of factors determining water quality, large variations are found between rivers or lakes on different continents or in different hydroclimatic zones.

Similarly, the response to anthropogenic impacts is also highly variable. As a

consequence, there is no universally applicable standard which can define the baseline chemical or biological quality of waters. At best, a general description of some types of rivers, lakes or aquifers can be given.

Although the major proportion of all water quality degradation world-wide is due to anthropogenic influences, there are natural events and environmental catastrophes which can lead, locally, to severe deterioration of the aquatic environment. Hurricanes, mud flows, torrential rainfalls, glacial outbursts and unseasonal lake overturns are just a

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few examples. Some natural events are, however, aggravated by human activities, such as soil erosion associated with heavy rainfall in deforested regions. Restoration of the natural water quality often takes many years, depending on the geographical scale and intensity of the event. The eruption of Mount Saint Helens, USA in 1980, and the

subsequent mud flows, are still having a profound effect on downstream water quality (D.

Rickert, US Geological Survey, pers. comm.).

Figure 1.4. A schematic representation of the statistical distribution of natural waters on a global scale and their suitability for different uses as defined by guideline and maximum allowable concentrations (MAC). A. An element of single natural origin (e.g. K⁺) and with concentrations always within guideline values. B.

An element of more than one natural origin (e.g. Na⁺) which can occur in concentrations which restrict its use or are too high for most purposes

1.4. Pollutant sources and pathways

In general, pollutants can be released into the environment as gases, dissolved substances or in the particulate form. Ultimately pollutants reach the aquatic environment through a variety of pathways, including the atmosphere and the soil.

Figure 1.5 illustrates, in schematic form, the principal pathways of pollutants that influence freshwater quality.

Pollution may result from point sources or diffuse sources (non-point sources). There is no clear-cut distinction between the two, because a diffuse source on a regional or even local scale may result from a large number of individual point sources, such as

automobile exhausts. An important difference between a point and a diffuse source is that a point source may be collected, treated or controlled (diffuse sources consisting of many point sources may also be controlled provided all point sources can be identified).

The major point sources of pollution to freshwaters originate from the collection and discharge of domestic wastewaters, industrial wastes or certain agricultural activities, such as animal husbandry. Most other agricultural activities, such as pesticide spraying or fertiliser application, are considered as diffuse sources. The atmospheric fall-out of

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pollutants also leads to diffuse pollution of the aquatic environment. The various sources of major pollutant categories are summarised in Table 1.4 and examples of pollution sources for groundwater are presented in Table 9.7.

Figure 1.5. Potential pollutant pathways related to the aquatic environment

Atmospheric sources

The atmosphere is proving to be one of the most pervasive sources of pollutants to the global environment. Significant concentrations of certain contaminants are even being observed in Arctic and Antarctic snow and ice, with high levels of bioaccumulation magnified through the food chain to mammals and native human populations (see Chapter 5). Sources of anthropogenic materials to the atmosphere include:

• combustion of fossil fuels for energy generation,

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• combustion of fossil fuels in automobiles, other forms of transport, heating in cold climates and industrial needs (e.g. steel making),

• ore smelting, mainly sulphides,

• wind blown soils from arid and agricultural regions, and

• volatilisation from agriculture, from waste disposal and from previously polluted regions.

Table 1.4. Anthropogenic sources of pollutants in the aquatic environment Source Bacteria Nutrients Trace

elements

Pesticides/herbicides Industrial organic

micro pollutants

Oils and greases

Atmosphere x xxxG xxxG xxxG

Point sources

Sewage xxx xxx xxx x xxx

Industrial effluents

x xxxG xxxG xx

Diffuse sources

Agriculture xx xxx x xxxG

Dredging x xxx xx xxx x

Navigation and harbours

x x xx x xxx

Mixed sources Urban run-off and waste disposal

xx xxx xxx xx xx xx

Industrial waste disposal sites

x xxx x xxx x

x Low local significance

xx Moderate local/regional significance xxx High local/regional significance G Globally significant

These sources, together, provide an array of inorganic and organic pollutants to the atmosphere which are then widely dispersed by weather systems and deposited on a global scale. For example, toxaphene and PCBs (poly-chlorinated biphenyls) have been described in remote lake sediments from Isle Royale, Lake Superior (Swaine, 1978) and in high Arctic ice (Gregor and Gummer, 1989). In the former case, the source was postulated as the southern USA and Central America, whereas in the latter case, the source was believed to be Eastern Europe and the former USSR. Deposition of pollutants from the atmosphere, either as solutes in rain or in particulate form, occurs evenly over a wide area; covering soils, forests and water surfaces, where they become entrained in both the hydrological and sedimentary (erosion, transport and deposition)

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cycles. This may be termed secondary cycling, as distinct from the primary cycle of emission into the atmosphere, transport and deposition.

Point sources

By definition a point source is a pollution input that can be related to a single outlet.

Untreated, or inadequately treated, sewage disposal is probably still the major point source of pollution to the world’s waters. Other important point sources include mines and industrial effluents.

As point sources are localised, spatial profiles of the quality of the aquatic environment may be used to locate them. Some point sources are characterised by a relatively constant discharge of the polluting substances over time, such as domestic sewers, whereas others are occasional or fluctuating discharges, such as leaks and accidental spillages. A sewage treatment plant serving a fixed population delivers a continuous load of nutrients to a receiving water body. Therefore, an increase in river discharge causes greater dilution and a characteristic decrease in river concentration. This contrasts with atmospheric deposition and other diffuse sources where increased land run-off often causes increased pollutant concentrations in the receiving water system.

Non-atmospheric diffuse sources

Diffuse sources cannot be ascribed to a single point or a single human activity although, as pointed out above, they may be due to many individual point sources to a water body over a large area. Typical examples are:

• Agricultural run-off, including soil erosion from surface and sub-soil drainage. These processes transfer organic and inorganic soil particles, nutrients, pesticides and herbicides to adjacent water bodies.

• Urban run-off from city streets and surrounding areas (which is not channelled into a main drain or sewer). Likely contaminants include derivatives of fossil fuel combustion, bacteria, metals (particularly lead) and industrial organic pollutants, particularly PCBs.

Pesticides and herbicides may also be derived from urban gardening, landscaping, horticulture and their regular use on railways, airfields and roadsides. In the worst circumstances pollutants from a variety of diffuse sources may be diverted into combined storm/sewer systems during storm-induced, high drainage flow conditions, where they then contribute to major point sources.

• Waste disposal sites which include municipal and industrial solid waste disposal facilities; liquid waste disposal (particularly if groundwater is impacted); dredged

sediment disposal sites (both confined and open lake). Depending on the relative sizes of the disposal sites and receiving water bodies, these sources of pollution can be considered as either diffuse or point sources, as in the case of groundwater pollution (see Table 9.7).

• Other diffuse sources including waste from navigation, harbour and marina sediment pollution, and pollution from open lake resource exploitation, in particular oil and gas (e.g.

Lakes Erie and Maracaibo).

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The time variability of pollutant release into the aquatic environment falls into four main categories. Sources can be considered as permanent or continuous (e.g. domestic wastes from a major city and many industrial wastes), periodic (e.g. seasonal variation associated with the influx of tourist populations, or food processing wastes), occasional (e.g. certain industrial waste releases), or accidental (e.g. tank failure, truck or train accidents, fires, etc.). The effects of these various types of pollutants on receiving water bodies are rather different. The continuous discharge of municipal sewage, for example, may be quite acceptable to a river during high discharge periods when dilution is high and biodegradation is sufficient to cope with the pollution load. During low discharges, however, pollution levels and effects may exceed acceptable levels in downstream river stretches. Figure 1.6A shows these two seasonal situations for rivers. The example of the effects of an episodic pollution event on a lake is given in Figure 1.6B which shows the influence of residence time on the elimination of the pollutant from the lake, as measured at its natural outlet. Lake volume and initial dilution are also factors co- determining the prevalence of the pollutant in the lake.

1.5. Spatial and temporal variations

Spatial variation in water quality is one of the main features of different types of water bodies, and is largely determined by the hydrodynamic characteristics of the water body.

Water quality varies in all three dimensions (see section 2.2.1) which are further modified by flow direction, discharge and time. Consequently, water quality cannot usually be measured in only one location within a water body but may require a grid or network of sampling sites.

For practical purposes, i.e. to limit the number of sampling sites and to facilitate the presentation of data, some simplifications to the ideal sampling grid are used. Examples include longitudinal or vertical profiles as shown in Figure 1.7. Two-dimensional profiles are most suitable for observing plumes of pollution from a source, presenting the information either with depth or horizontally in the form of maps. These are particularly applicable to lakes, reservoirs and groundwater aquifers.

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Figure 1.6. The influence of hydrodynamic characteristics on the environmental fate of pollutants (CM maximum concentration reached, MAC maximum allowable

concentration) A. Schematic response observed at a given river station downstream of a chronic point source of pollution (PA) (non-reactive dissolved

substances). High (A₂) and low (A₁) river discharge. B. Schematic response observed at lake outlets following a single episode of pollution (PB) (non-reactive

dissolved substances) for long (B₁) and short (B₂) residence times in lakes of equal volumes

The temporal variation of the chemical quality of water bodies can be described by studying concentrations (also loads in the case of rivers) or by determining rates such as settling rates, biodegradation rates or transport rates. It is particularly important to define temporal variability. Five major types are considered here:

• Minute-to-minute to day-to-day variability resulting from water mixing, fluctuations in inputs, etc., mostly linked to meteorological conditions and water body size (e.g.

variations during river floods).

Water Quality Assessments - A Guide to Use of Biota, Sediments and Water in Environmental Monitoring - Second Edition